The Sons of Liberty in Boston received intelligence that the British were moving troops into the countryside. Arrangements were made to alert the populace...
https://www.paulreverehouse.org/the-real-story/
On the early morning of the 19th, the British troops marched into Lexington. Standing on the Green to oppose them were a line of Minutemen under the command of Captain John Parker. Seeing the British Regulars in full battle array, he said to his outnumbered men: “Stand your ground. Do not fire unless you are fired upon, but if they mean war, let it begin here.”
https://www.battlefields.org/learn/articles/lexington-and-concord-shot-heard-round-world
